Lithography is widely recognized as one of the key steps in the manufacture of integrated circuits (ICs) and other devices and/or structures. However, as the dimensions of features made using lithography become smaller, lithography is becoming a more critical factor for enabling miniature IC or other devices and/or structures to be manufactured.
A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of ICs. In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. including part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned.
In a lithographic apparatus, many moving parts are typically provided with various degrees of freedom, and the motions and locations (including linear and angular positions (orientation), velocities and accelerations) are controlled automatically via numerous actuation mechanisms (actuators). Actuators may be electromagnetically, pneumatically, or hydraulically operated. Actuators are often constrained to effect movement in only one degree of freedom (linear or rotational). Where the moving parts are to be controlled in a plurality of degrees of freedom, more complex mechanisms may be provided, or multiple single-degree mechanisms may be combined.
In order to shorten the exposure wavelength and, thus, reduce the minimum printable size, it has been proposed to use an extreme ultraviolet (EUV) radiation source. EUV radiation sources are typically configured to output radiation wavelengths of around 5-20 nm, for example, 13.5 nm or about 13 nm or 6.5-6.8 nm. Use of EUV radiation may constitute a significant step toward achieving small features printing. Such radiation is termed extreme ultraviolet or soft x-ray, and possible sources include, for example, laser-produced plasma sources, discharge plasma sources, or synchrotron radiation from electron storage rings. Because of the desire for extreme accuracy, and because additionally of the desire to work in a vacuum environment with high reliability, designing actuators for EUV lithography apparatus is particularly challenging.